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Matthew Lim’s PW-03 is a hand-cranked, six-digit mechanical calculator built from more than 130 custom-designed parts. It uses adjustable pinwheels to enter numbers, an accumulator to hold results, and a rotation counter to track operations. According to CircuitDigest’s October 1, 2026 report, it handles addition and subtraction directly, then uses repeated addition or subtraction for multiplication and division. Lim’s project listing confirms the machine’s four arithmetic functions and says it uses no electronics or motors.
How the PW-03 performs arithmetic
The PW-03’s logic is mechanical: moving parts transmit each crank turn through the input and accumulator. CircuitDigest describes four adjustable pinwheels, each with movable pins set from 0 to 9, and a system for resetting the machine. Lim’s listing identifies the main assemblies as a pinwheel input, six-digit accumulator, rotation counter, and two handles.
Addition and subtraction
To add, the operator sets the pinwheel input to a number and turns the crank. The mechanism transfers that value into the accumulator. Turning the crank in the opposite direction subtracts instead. These are direct operations; the user supplies the entered value and direction through the controls.
Multiplication
Multiplication works through repeated addition, according to CircuitDigest. The pinwheel assembly can be repositioned by decimal place, allowing the operator to apply the appropriate place value while accumulating the result. The rotation counter records crank turns, but the report does not provide a tested speed or an accuracy rating.
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Division
For division, the operator repeatedly subtracts the divisor from the number in the accumulator. The rotation counter tracks the number of subtractions as the quotient, while the accumulator retains the remainder. This approach makes division a sequence of mechanical operations rather than a single electronic calculation.
What went into the design
CircuitDigest reports that the calculator contains more than 130 custom-designed parts and that Lim developed more than 30 versions of the carry mechanism before changing it to use ball springs and smoother moving surfaces. The report says high-precision resin printing helped with small moving pins that could catch on FDM print layer lines, while tough resin was used for parts subject to repeated flexing or force.
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Those material details describe the design process as reported by CircuitDigest. Lim’s project listing, by contrast, gives settings for a reference build made with filament. The two accounts should not be read as a single universal material specification for every printed part or build.
Build requirements and listed print settings
Lim describes the build as difficult and sensitive to low tolerances. The project listing recommends a well-calibrated printer with a build area of at least 180 × 180 mm and approximately 450 g of filament in two colours; it says basic PLA works. The listed reference build used a Bambu Lab P2S and Bambu Lab A1.
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| Part category | Project-listing setting |
|---|---|
| Precision parts | 0.12 mm layer height |
| Other parts | 0.16 mm layer height |
| Outer cover | 0.20 mm layer height |
| Walls and infill | Three walls; 15% cross-hatch infill |
These are the creator’s recommended settings for the listed project, not guaranteed settings for every printer, material, or slicer. A machine with inconsistent extrusion or poorly calibrated dimensions may struggle with parts whose clearances are small.
Hardware checklist
The project listing specifies these external components:
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- 46 M2 × 4 mm screws
- 42 M2 × 6 mm screws
- Five M2 × 14 mm screws
- Two M2 × 20 mm screws
- Fifteen 3 × 4 mm ball spring plungers
- Ten 5 × 2 mm magnets
Lim specifically names the Bambu Lab Smooth Ball Spring Plunger and warns that alternatives with similar nominal dimensions may differ slightly and fail to seat correctly. Treat that as a compatibility requirement when following the project listing, rather than assuming any similarly sized plunger will fit.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Where the mechanism fits in calculator history
CircuitDigest attributes the PW-03’s inspiration to historic mechanical calculators, particularly the pinwheel mechanism associated with Willgodt Odhner. The Odhner Arithmometer is likewise identified as a pinwheel-mechanism calculator by the specialist calculator reference. That connection provides context for the mechanism; it does not establish that Lim’s modern design reproduces a specific historical model.
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Getting the project files
Lim’s project listing offers STL files, pre-arranged project files, and an illustrated step-by-step guide. Check that listing for current access, price, and licence terms. It states that the files are for personal, non-commercial use and prohibits resale, redistribution, and commercial use; consult the creator’s page for the wording that applies when obtaining the files.
The available sources describe the design and its recommended build specifications, but do not establish independent accuracy testing, reliability across a test suite, or results from other builders. The PW-03 is therefore best understood as a complex maker project demonstrating mechanical arithmetic, not as a performance-validated replacement for an electronic calculator.
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